The present invention pertains to packet data communication systems and more particularly to Session Initiation Protocol based retries of communication between a network and a user.
Session Initiation Protocol (SIP) over Internet protocol (IP) is commonly used in packet data networks to provide services including voice to wireless or mobile users. Session Initiation Protocol provides for certain methodology to retry an attempted communication between a server and a mobile unit (SIP invite request).
When using User Datagram Protocol (UDP) as a transport protocol, SIP employs retransmission request procedures to insure reliable transfers among networks and between the network and a user. Currently SIP provides for a retransmission time period which increases on an exponential basis. That is, the SIP protocol waits for approximately one-half second before retransmitting a message. For a retransmission and each successive retransmission, the SIP protocol doubles the time interval. For example, the original one-half second wait from the initial transmission would be doubled to one second before the second retransmission of a message. The retransmission time period would then be doubled successively until a response is received or a final response time out condition occurs.
When SIP is used over a wireless system, such as a CDMA (Code Division Multiple Access) system the response times typically become larger since the mobile user may be in an idle or dormant state and must be connected over an air interface (wireless). For such mobile users there is a very high probability that connection and response to the initial invite message or several of the retry messages will not occur within a time expected by the standard SIP response timers. As a result more retry transmissions will occur over the air interface.
Accordingly, it would be desirable to have a retransmission method which is customized for the applicable interface environment thereby lowering the traffic through the system and network.